Protease inhibitors are potent antiretroviral agents that delay the progression of HIV disease, yet they are clinical failures because retroviral resistance is becoming more common. In this protocol, the genotypic and phenotypic correlates of protease failure are being explored, as are other causes of drug failure such as drug interactions and poor absorption. The activity in vivo of an experimental nucleoside and an experimental protease inhibitor are being examined. Drugs and strategies for reducing viral burden in these apparent virologic failures will be assessed. Resistance to marketed protease inhibitors is a major problem that is likely to reduce the hopes associated with current therapies. Prompt evaluation of agents for patients with HIV is a high priority for salvage therapy.